US regulator's nod for smallpox drug

US regulators have approved the first treatment for smallpox - a deadly disease that was wiped out four decades ago - in case the virus is used in a terror attack.

Smallpox, which is highly contagious, was eradicated worldwide by 1980 after a huge vaccination campaign.

But people born since then haven't been vaccinated, and small samples of the smallpox virus were saved for research purposes, leaving the possibility it could be used as a biological weapon.

Maker SIGA Technologies of New York has already delivered two million treatments that will be stockpiled by the government, which partially paid for the development of the drug, called TPOXX.

A man, who has contracted small pox, is shown with a formation of scar-producing pustules on his body on Nov. 1, 1941. The New York State Board of Health anti-disease campaign used this image in 1941 to encourage the public to vaccinate in New York and other states with the caption, "This man was never vaccinated against smallpox." (AAP) (AAP)

To test the drug's effectiveness, monkeys and rabbits were infected with a similar virus and then given the drug. More than 90 per cent survived, the company said. Its safety was tested in several hundred healthy volunteers, who were not infected with smallpox.

Smallpox killed about 300 million people worldwide in the 20th century before its eradication.

Symptoms include fever, fatigue and pus-filled sores. Until now, doctors could only provide supportive care such as IV fluids and fever remedies and isolate the patients. Vaccination can be used to prevent infection but it must be done within five days of exposure to the virus, well before symptoms appear.